This invention relates to an analog to digital converter and a system for controlling the envelope of a periodic waveform using such a converter.
Conventional commercially available integrated circuit analog to digital converters are only able to digitize signals up to approximately 1 GHz bandwidth. However, there is a requirement for digitizing wide bandwidth periodic analog electrical signals in a system that corrects ripple on the input signal. Such signals typically have a 5 GHz bandwidth or greater, which existing systems cannot deal with. In specialist test equipment, wide bandwidth signals up to 50 GHz have been digitized, but the equipment is bulky, costly and has a high power requirement. These drawbacks make this type of equipment unsuitable for use in tightly integrated, low-power systems. Such prior art ADCs operate by sampling the input signal over a very short time window, and digitizing the sample with a high resolution ADC that does not have the required input bandwidth. ‘Equivalent-time sampling’is a technique that can then be used to measure the complete waveform.
There are existing A/D converters which operate by splitting an input signal into multiple signals and sampling these in parallel. This creates multiple high fidelity copies of the input signal. However, this method cannot be used at microwave frequencies because of difficulties in sampling all the channels together.